Investigating the Influence of Incorporation of Boron Nitride on the Kinetics of Isotactic Polypropylene Entanglement Recovery

Abstract

Highly filled polymers with low viscosity and high melt flow rate (MFR) are in great demand for favorable processability. Disentanglement by the treatment of external processing fields usually can reduce the viscosity to meet the processing requirements. This work tries to evaluate the influence of hexagonal boron nitride (BN) on the kinetics of isotactic polypropylene (PP) entanglement recovery. The results show that polypropylene/boron nitride (PP/BN) composites after the shear experiment on a parallel-plate rotational rheometer can be kept in a low-viscosity state for a long time, indicating that the presence of BN effectively maintains the disentangled state of PP/BN composites. At the same time, the MFR of PP/BN composites with a diameter of 15 μm BN, which has the best effect of inhibiting entanglement recovery, increases from 1.62 to 3.51 g/10 min after the shear experiment. As for PP, the complex viscosity quickly recovers to its original state and the MFR has no obvious change. Consequently, it is possible to realize highly filled polymer disentanglement to meet the post-processing.

The all‐polymer composites and blends made of ethylene–octene copolymer and partially disentangled polypropylene using a new processing approach

“…Some interesting results have been published recently. [19][20][21][22][23][24][25][26] For example, it has been found that partial disentanglement of polymer such as polylactide (PLA) can promote the distribution of multi-walled carbon nanotubes (MWCNTs) during composite extrusion. 20 Better dispersion of MWCNTs resulted in an increase in the elastic modulus and stresses measured in the tensile test as well as the additional nucleation during crystallization.…”

“…Entanglement recovery was also investigated after incorporating a large amount (35%) of boron nitride into polypropylene and disentangling it by a constant shear process. 23 The filler particles effectively maintained the disentangled state by attaching molecular chains to the particle and limiting their mobility. In the tested composites, the viscosity was constant for at least 300 s.…”

“…Although research on the properties of partially disentangled homo polymers has provided basic knowledge about this group of materials, only a small number of publications describe the use of partially disentangled polymers for the production of polymer composites and polymer blends. Some interesting results have been published recently 19–26 . For example, it has been found that partial disentanglement of polymer such as polylactide (PLA) can promote the distribution of multi‐walled carbon nanotubes (MWCNTs) during composite extrusion 20 .…”

Regulation of Entanglement Networks under Different Shear Fields and Its Effect on the Properties of Poly(l-lactide)

“…The crucial issue is how to effectively achieve melt disentanglement and retain it in pellet for the next secondary processing. Despite the fact that shear thinning is observed in conventional processing methods, it does not mean that disentanglement can be achieved by simple injection or extrusion because disentanglement is related to the time and method of shearing. − It is noteworthy that the work of Ibar states that shear thinning is a transient behavior, while disentanglement that occurs during sustained shear should take into account both strain softening and shear thinning. − The results of many studies demonstrate that the melt elasticity and viscosity of the preshear-treated polymer samples are reduced to some extent, the properties of which gradually become identical to those of the untreated one with increasing heat treatment time. ,,− Moreover, the re-entanglement process of the disentangled chain can be monitored in situ for some materials by time-scan rheological measurements after preshearing by a rotational rheometer, i.e., the modulus and viscosity slowly return to their initial values once shear has stopped, which supports the idea that the disentangled state can be maintained in pellet for later processing. − …”

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

“…Polypropylene (PP) is one of the most widely used thermoplastic polymers across the world and has been employed in the fields of construction, textile, packaging, electrical, and automotive industries – owing to its good comprehensive performance and low cost. – To obtain higher mechanical properties, elastomers such as polyolefin elastomer (POE) and ethylene–propylene random copolymer (EPR) are often blended with PP. – Injection molding is one of the most popular industrial manufacturing technologies because of its advantages of mass production, repeatability, automation, and accuracy. Nowadays, large injection molded products of PP/elastomer blends are increasingly applied in automobiles, such as car bumpers, dashboards, door panels, and other interior pieces. , In addition to meeting the requirements of mechanical properties, such as toughness, strength, etc., these products are also supposed to have an aesthetically pleasing appearance.…”